Bitter principles in citrus juices and their products are flavanoids, predominantly naringin, and/or limonoids, predominantly limonin. The chemistry and properties of these principles have been discussed in detail by J. F. Kefford and B. V. Chandler in Chapters 13 and 14 of "The Chemical Constituents of Citrus Fruits" (Academic Press, 1970); V. P. Maier, R. B. Bennett and S. Hasegawa; and R. M. Horowitz and B. Gentili in Chapters 9 and 10 of "Citrus Science and Technology" Volume I (AVI Publishing Company, 1977) respectively; and N. A. Michael Eskin in Chapter 5. of "Plant Pigments, Flavors and Textures: The Chemistry and Biochemistry of Selected Compounds" (Academic Press, 1977). The presence of bitterness is often accentuated by processing of the fruit to juice or concentrate and thus many wholesome fruits with skin blemishes are wasted because they can neither be used as fresh fruit nor can they be processed into juice.
Flavanoid bitterness is generally due to the presence of naringin (4', 5, 7,-trihydroxyflavanone-7 rhamnoglucoside). Naringin is distributed throughout the fruit, but occurs in highest concentration in the albedo. Several methods have been proposed for the reduction of naringin in citrus juices. These methods are based on the enzymatic modification of naringin to nonbitter compounds, by the action of the enzyme naringinase. D. Dinelli and F. Morisi (French Patent No. 2,125,539) discloses the use of naringinase immobilized on cellulose esters to debitter grapefruit juice. M. Ono, T. Toso and I. Chibata used naringinase immobilized on DEAE-Sephadex to debitter Natsudaidai juice (J. Fermt. Technol, Vol 55, p. 493-500, 1977). A. C. Olson, G. M. Gray and D. G. Guadagni debittered grapefruit juice using naringinase immobilized in hollow fibres (J. Food Sci., Vol. 44, p. 1358-1361, 1979). While these techniques have been used to reduce naringin in citrus juices, they are limited in their application due to factors such as the unavailability of purified enzymes in commercial quantities, low reaction rates associated with immobilized enzymes and inadequate half life of immobilized enzymes.
Limonoid bitterness is due to the presence of the dilactone, limonin. Limonin is formed from its nonbitter precursor-limonin A-ring lactone, which is initially present in the albedo of citrus fruits. The formation of limonin from its precursor takes place in the presence of an acidic environment or upon heating. Therefore, processes of juice extraction, heat treatment, and storage of juice or concentrate result in limonin induced bitterness, especially in early season orange, Navel orange and lemon juices. Limonin levels in excess of 6 p.p.m. are detectable as bitterness.
Several approaches have been attempted to control limonin induced juice bitterness. These include preharvest considerations such as plant growth regulators, rootstocks, and a variety of other horticultural factors (R. F. Albach, G. H. Redman, and G. J. Lime in "Limonin Content of Juice from Marrs and Hamlin Oranges (Citrus sinensis (L.) Osbeck)." J. Agric. Food Chem., Vol 29, p. 313 to 315, 1981); postharvest fruit treatments with ethylene and plant growth regulators (V. P. Maier, L. C. Brewster and A. C. Hsu in "Development of Methods for Producing Non-Bitter Navel Orange Juice." Citograph Vol 56, p. 373 to 375, 1971): the use of relatively low pressures in juice extraction to prevent disruption of the albedo (J. H. Tatum and R. E. Berry in "Method for Estimating Limonin Content of Citrus Juices." J. Food Sci., Vol 38, p. 1244 to 1246, 1973); adsorption of limonin on polyamides (B. V. Chandler, J. F. Kefford and G. Ziemelis in "The Removal of Limonin from Bitter Orange Juice" in J. Sci. Food Agric., Vol 19, p. 83 to 86, 1968); adsorption of limonin on cellulose esters (B. V. Chandler and R. L. Johnson, U.S. Pat. No. 3,989,854, 1976); enzymatic approaches (S. Hasegawa in "Metabolism of Limonoids, Limonin D-Ring Lactone Hydrolase Activity in Pseudomonas" in J. Agric. Food Chem., Vol 24, p. 24 to 26, 1976); and the use of bitterness modulators such as neodiosmin (D. G. Guadagni, R. N. Horowitz, B. Gentili and V. P. Maier, U.S. Pat. No. 4,154,862, 1977).
U.S. Pat. No. 2,681,907; Kunin, "Ion Exchange Resins," 2nd Edition, 1958, pp 87, 89; Gage et al, "Science," Volume 113, pp 522-523 (May 4, 1951); and "Chemical Abstracts," Volume 46, Abstract No. 6202f(19) disclose removing flavanoid compounds from aqueous solutions (including plant and vegetable extracts) by treatment with an ion exchange resin. All of these references specifically disclose the use of Amberlite IRC-50 as the ion exchange resin. As shown in Table 13 on page 89 of Kunin, Amberlite IRC-50 is a cation exchanger of the carboxylic (acrylic) type which, as further disclosed on page 87 of Kunin, is prepared by the copolymerization of either methacrylic acid or acrylic acid with divinyl-benzene. None of the above-listed references specifically disclose the treatment of citrus juices.
U.S. Pat. No. 4,282,264; French Patent No. 882,796; Swiss Patent No. 233, 394; Calmon et al., "Ion Exchangers in Organic and Biochemistry," 1957, pp 623-625; "Abstracts, 112th Meeting, ACS," September, 1947, page 5Q; and "Chemical Abstracts," Volume 40, Abstract 55039(19) disclose treating fruit or vegetable juices (including citrus juices) with ion exchange materials broadly.
U.S. Pat. Nos. 2,510,797 and 3,463,763 disclose debittering of citrus juices by treatment with various adsorbents which apparently do not have any ion exchange properties. More specifically, U.S. Pat. No. 2,510,797 discloses the use of activated carbon and U.S. Pat. No. 3,463,763 discloses the use of the resins polyhexamethylene adipamide and polyvinylpyrrolidone for such treatments.
The aforementioned methods have severe limitations and are not practical enough to warrant commercial application. The enzyme methods are especially undesirable because of the unavailability of economic, commercial quantities of enzymes.
Use of polyamides to debitter citrus juices results in a substantial loss of ascorbic acid from orange juice. Furthermore, a two-stage treatment of the juice is necessary due to the preferential adsorption of phenolic compounds by polyamides. This technique, therefore, would not appear to be economically advantageous.
Partial removal of flavanoids by contacting citrus juices with cellulose esters have been reported by K. S. Kealey and J. E. Kinsella in "Orange Juice Quality with an Emphasis on Flavor Components" in CRC Critical Reviews in Food Sci. & Nutrition, Vol 11, p. 1-40, 1979, with reference to U.S. Pat. No. 3,989,854 to Chandler, et al.
U.S. Pat. No. 3,989,854 teaches adsorption of limonin from fruit juices but not naringin adsorption on cellulose esters. Said patent discloses that cellulose esters successfully debitter navel orange juice by adsorbing limonin. However, nowhere is it disclosed or suggested that the adsorption technique can be used successfully to debitter juices/products in which naringin, or naringin in conjunction with limonin induces the bitterness. The application of cellulose esters to debitter citrus juices is thus limited to products in which the bitterness is induced solely by limonin.
The use of neodiosmin as a bitterness modulator has not found industrial application. Neodiosmin is not approved for use as a food additive and is essentially ineffective when compounds causing the bitterness are present at high levels.
Japanese Laid-Open Patent Application No 18971 Jan. 30, 1982 discloses a process for producing a citrus fruit juice which comprises the steps of subjecting fruit juice prepared by squeezing and separating in a conventional manner and sterilized as required by centrifugal separation or enzymatic treatment followed by filtration to obtain a fruit juice having insoluble solids contents of less than 0.5% (v/v), then treating same with anion exchange resins, and mixing the thus acid removed fruit juice with a nonacid removed fruit juice having insoluble solids content of more than 0.5% (v/v) in an adequate amount. Exemplied is use of an anion exchange resin regenerated with an aqueous sodium hydroxide solution.
Some persons exhibit a low tolerance to highly acidic fruit juices and therefore would prefer a reduced acid product, such as reduced acid grapefruit or orange juice. We have observed that removal of some of the acid from grapefruit juice by ion exchange, for example, seems to intensify the sensation of bitterness several fold. Therefore, in order to prepare a deacidified citrus juice, especially grapefruit juice, it is especially desirable to employ a process for debittering the juice, before or after deacidification.